This ash cloud load graphic is the output of a mathematical model of volcanic ash transport in the atmosphere (Ash3D, USGS).

This model shows expected load (amount) of ash in the atmosphere for actual or hypothetical eruptions.

AVO produces this graphic when a volcano is restless by assuming a reasonable hypothetical eruption, in order to provide a pre-eruptive forecast of airspace likely to be affected. During an eruption, AVO updates the forecast with actual observations (eruption start time and duration, plume height) as they become available.

Colors represent amounts of ash in the atmosphere, summed from the bottom to the top of the cloud. Warmer colors represent areas of greater ash; colder colors mean less ash.

This graphic does not show ashfall deposition on the ground; go here for ashfall graphic. Note that it is possible for ash clouds to move overhead with little or no fallout on the ground.